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Old 21st November 2003, 12:36 AM   #1
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Default Need to connect mute pin on 3886?

Just wondering if you need to connect the mute pin on the lm3886 in order for the amp to work. Its the only thing I can think of, mine is unconnected right now. The amp doesn't have any output.

Also, when I turn my amp on and measure the V+ and V-, I get +40V and -14V. Is this normal at idle? I also accidently hooked the transformer up backwards and got +1.4V and -54V the first time, which may have fried my amp, but i heard these things are pretty resiliant to overloads and stuff.

Heres the schematic from national.
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Old 21st November 2003, 12:50 AM   #2
ddog is offline ddog  Finland
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Yes, you have to connect it with resistor between Mute pin and -V, value calculated so 0,5mA or greater can be drawn from Mute pin.

+V = 40V and -V= -14V doesn't seem normal to me. Are supply electrolyts connected correctly?
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Old 21st November 2003, 12:52 AM   #3
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LM3886 Mute Disable
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Old 22nd November 2003, 01:32 AM   #4
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How did you make your power supply? Did you just use 2 caps, a transformer, and a rectifier? Do you have the schematic you used? Remove the power supply leads from the amp and test them with a multimedia. See what you get.

I think that the low - voltage is because you skipped connecting the mute pin and it is shorting the amp, though. did you skip any resistors/caps either? If so, which ones?
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Old 22nd November 2003, 08:41 AM   #5
Pan is offline Pan  Sweden
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Reversing the V+/- has probably fried your chip, happened to my friend when he mixed up the lines.

/Peter
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Old 24th November 2003, 02:07 PM   #6
macboy is offline macboy  Canada
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Quote:
Reversing the V+/- has probably fried your chip, happened to my friend when he mixed up the lines.
I agree. These things are pretty resilient when it comes to overheating, difficult loads, etc., but like virtually any semiconductor, reversing the voltage is a very bad thing.
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